Kamaraj M

Investigations have been carried out to study crack growth behaviour in type 304 stainless steel under constant-load creep conditions in the temperature range 550-650°C. At 550 and 600°C the load point deflection rate bears a unique relation to the creep crack growth rate, independent of the load. However, the results at 650°C show that the relation is load dependent. The parameters, stress intensity factor and net section stress, do not describe the crack growth rate well and there is wide scatter. The energy rate line integral C* appears to be applicable at 550 and 600°C but not at 650°C where it gives a systematic segregation of data. On the basis of a phenomenological approach a new parameter is derived which appears to correlate well with the creep crack growth at all the three temperatures investigated. This approach also provides an index which can differentiate between creep brittle and creep ductile materials. © 1987.

Type 308 stainless steel containing niobium is often used in high temperature applications. Welding is normally resorted to for joining purposes in such components. The crack growth behaviour in the weldment of 308 S.S. has been studied in the temperature range of 600 to 800°C. The stress intensity factor, the COD approach and the energy rate line integral have been tried to correlate the crack growth rate. Crack growth takes places along the interphase between the austenite and the primary arm of the delta ferrite at 600°C. At higher temperatures sigma phase becomes more dominant in the crack growth process. © 1989.

Defining a creep-brittle materialsas one in which the load point deflection rate is a function of the crack propagation rate only and is independent of the load or crack length, the applicability of C* to correlate the crack growth rate is discussed in this letter. © 1987.